A conductive planar crystal of SP2-bonded carbon atoms is called “graphene”. Graphene is described in detail in Kumi YAMADA, Kagaku to Kogyo (Chemistry and Industry), 61 (2008) pp. 1123-1127. Graphene is a basic unit of various forms of crystalline carbon films. Examples of crystalline carbon films formed of graphene include monolayer graphene formed of one layer of graphene, nanographene which is a nanometer-size stack of several layers to about ten layers of graphene, carbon nanowall (see Y. Wu, P. Qiao, T. Chong, Z. Shen, Adv. Mater. 14 (2002) pp. 64-67) which includes a graphene stack including several layers to about ten layers of graphene and is located at an angle close to 90 degrees with respect to a substrate surface, and the like.
A crystalline carbon film formed of graphene is expected to be used for a transparent conductive film or a transparent electrode owing to a high light transmittance and a high electric conductivity thereof. In addition, the carrier mobility of electrons and holes in graphene may be possibly 200,000 cm2/Vs at the maximum, which is 100 times as high as that of silicon at room temperature. Utilizing this property of graphene, a super high-speed transistor operable at a rate of the order of terahertz is being developed.
For producing graphene, various methods have been developed so far, including a method of peeling off graphene from natural graphite, a method of treating silicon carbonate at a high temperature to cause silicon to be desorbed, a method of forming graphene on a surface of various types of metal materials, and the like. Regarding a transparent conductive carbon film using a crystalline carbon film formed of graphene, a wide variety of industrial uses have been examined. For realizing such uses, a method for producing a graphene film in a large area size at a high throughput is now desired.
Recently, methods of producing graphene by chemical vapor deposition (CVD) performed on a copper foil surface have been developed (Non-patent Xuesong Li, Weiwei Cai, Jinho An, Seyoung Kim, Junghyo Nah, Dongxing Yang, Richard Piner, Aruna Velamakanni, InhwaJung, Emanue L Tuluc, Sanjay K. Banerjee, Luigi Columbo, Rodney S. Ruoff, Science, Vol. 324, 2009, pp. 1312-1314, and Xuesong Li, Yanwu Zhu, Weiwei Cai, Mark Borysiak, Boyang Han, David Chen, Richard D. Piner, Luigi Colombo, Rodney S. Ruoff, Nano Letters, Vol. 9, 2009, pp. 4359-4363). Such a method of producing a graphene film by use of a copper foil as a substrate adopts a thermal CVD method. More specifically, methane gas, which is material gas, is thermally decomposed at about 1000° C. to form one to several layers of graphene on the copper foil.
The above-mentioned method of producing graphene by CVD basically uses a gas-form material such as methane gas or the like. For producing graphene, various solid materials such as various reins and the like may be used, but it is difficult to use these materials for CVD. In addition, with CVD using gas as a material, it is difficult to produce graphene on a specific part of the substrate in a specific pattern. Therefore, graphene needs to be processed to be patterned after being produced on the substrate. In order to solve these problems, a method of forming graphene by a resin carbonization method has been recently developed. According to this method, poly(methyl methacrylate) (PMMA) is applied to a copper foil to form a PMMA film, and the PMMA film on the copper foil is heated at 800° C. to 1000° C. in a mixed gas atmosphere of hydrogen and argon (ZhengzongSun, Zheng Yan, Jun Yao, Elvira Beitler, Yu Zhu, James M. Tour, NATURE, doi:10.1038/nature09579).